Aviation-mad pensioner Myrtle Rose has spoken of her encounter with US fighter jets as she unwittingly strayed into restricted airspace during Barack Obama's visit to Chicago.

The 75-year-old was taking a short flight over suburban Chicago when she looked out her cockpit window to see two F-16s, but assumed the US Air Force pilots were just slowing down to get a closer look at her 1941 Piper J-3 Cub plane.

It was not until she landed that friends and police told her the attention was much more serious - for straying into restricted airspace during a visit by the US president.

Ms Rose, who tries to fly every day, said she had been itching to get back in the air on Wednesday after a number of days on the ground. She said she normally used her computer to check for airspace restrictions, but it was not working properly.

"I hadn't flown in over a week," she said. "It was a beautiful afternoon." After some guests left her home, she "just climbed in the vintage plane and left". To make matters worse, she said, "I didn't have my radio on. I was just flying around".

On any other day, the brief flight would never have attracted notice. However, Mr Obama was in Chicago for a Democratic fund-raising event marking his 50th birthday.

But Lt Col Mike Humphreys, a spokesman for the North American Aerospace Defence Command, which scrambled the two warplanes - a proposition that costs 9,000 dollars (£5,500) an hour per jet - said: "There's really no excuse for not knowing. Anyone who flies an aircraft should know the restrictions."

Ms Rose said she was about 30 miles from O'Hare Airport when her plane was intercepted but as the fighters appeared, she was not alarmed.

"I thought, 'Oh, well, they're just looking at how cute the Cub is'," she said.

The blue-and-yellow plane had won a best-in-class award at the Oshkosh Air Show, a huge annual gathering in Wisconsin.